Differential pressure switches are desirable in maintaining a predetermined pressure balance between opposing sources of fluid pressure. In general, an outlet from each pressure source is attached to a fluid/mechanical interconnection, such as a piston, that is, itself interconnected with a switch. As long as a predetermined balance is maintained, the piston remains stationary with the pressure induced forces in relative equilibrium and the switch carries a constant state. However, if the balance or difference of pressure becomes disturbed or altered relative to a predetermined value, the piston moves and, if the movement passes a given threshold value, the switch trips, changing the switch's state to generate an appropriate signal. The signal may include an alarm that an operator acts upon manually, or a control for automatic devices.
In a popular form of pressure switch that utilizes a moving piston disposed between a pair of outlets, switch contacts that are placed in alignment with the piston connect and disconnect alternatively in response to the piston's pressure induced movement. The alignment of contact circuitry directly with the piston, however, renders adjustment of gain or sensitivity more difficult and increases the complexity of the piston mechanism. The location of the switch and its circuitry proximate the piston also entails the use of the already limited space in the piston bore, thus making the inclusion of standardized electrical components more difficult. Additionally the placement of circuitry in direct contact with the fluid/mechanical elements increases the risk of their damage and long term degradation.